Conservative party conferences increasingly resemble the French national assembly in the early 1790s. Those who passionately applaud the speakers of today scarcely trouble to conceal their expectation that tomorrow the same heroes will occupy tumbrils rattling through the streets to kiss Madame Guillotine. Cameron looks like a man who hears tumbrils, or at least the embittered party faithful baying for blood rather than a higher threshold for inheritance tax.

"Of course we must back David all the way to the election," a party donor said to me last week. "After that ..." He passed a hand across his throat. I suggested to a prominent Tory strategist that Cameron should have the chance to lose one election without automatically forfeiting his job. Some of us have always believed the party faces too high a mountain to gain power next time, even under the leadership of a Caesar.

My friend laughed derisively. "The party will never stand for keeping Cameron if he loses," he said. "He'll have to go." The wife of a former Tory cabinet minister says that her aunt, a caricature Disgusted of Tunbridge Wherever, thinks Gordon Brown is wonderful. A tycoon who for years raised money for the Tories says he will certainly vote for Brown, because Labour's leader is much more rightwing than Cameron.

It is all pretty mad. Here is this host of people who profess to want Labour out of office. Cameron is the only plausible alternative in town. Yet before an election is even called, a substantial part of his own party regards him with less respect than it does Brown.

Some will derive a masochistic satisfaction from seeing the prime minister trounce him at the polls. Through the arid years ahead, while chafing at the perceived shortcomings of Brown's Britain, they will say to each other: "It's all that bugger Cameron's fault."

In truth, of course, the extraordinary political state of Britain is chiefly attributable to national prosperity, which makes a governing party almost unassailable. People profess to be angry about Iraq, pensions, the bloated public payroll, the destruction of local government, education policy, inheritance tax, uncontrolled immigration and yobbish youth. Yet it all pales into insignificance alongside the fact that most voters feel well off. The middle middle class, people earning £30,000-60,000 a year, are squeezed. They could give Labour a bad time in the marginals. But a great many voters have never had it so good.

Because there is so much cash sloshing about, Brown's largely futile public spending spree has been affordable. It has seemed unnecessary to make hard choices about what needs to be done to keep this country competitive.

A few months ago I quoted on this page a Conservative grandee who told me exultantly that the Blair years have been "great for Britain". He meant, in truth, that he has become very rich. How can he and other Tories in Blackpool, who privately find life under Labour perfectly acceptable, mobilise genuine indignation towards the government, far less a scintilla of belief that their own party can win an election?

Cameron got one big thing right. Britain is now a social democratic country. In the absence of a national crisis, there are not enough right-inclined voters to elect a rightwing Tory government. He thus set out to build support beyond the old party laager. In the past two years, he has shown himself an enlightened, thoughtful and decent man.

Where has he gone wrong? Simon Jenkins rightly observes that modern elections are not decided by policies. They turn on the perceived characters of rival leaders. But it is prudent to ensure that such policies as an opposition party offers strike a chord with the electorate.

Cameron has wildly overdone his enthusiasm for greenery. His opposition to nuclear power, his espousal of pretty but politically idiotic Zac Goldsmith, have hurt him in middle England. There are nowhere near enough wind-turbine enthusiasts to vote the Tories in. Most people are environmental hypocrites. They accept in principle that they should be eco-friendly. But they don't want chastity yet.

When Cameron first became a leadership candidate, I was sceptical as to whether people were willing again to be ruled by young Etonians. Then it began to look as if voters cared less about which schools people had attended than whether they seem fit to run the country. Now, again, the Etonians feel wrong. There is a marshmallow quality about much of the Tory frontbench. They lack passion. They have, in Trollope's phrase, grown up on the sunny side of the wall. Perversely, Gordon Brown's rugged awkwardness becomes a kind of asset alongside the adolescent fluency of the Cameroonians.

I remain baffled by public enthusiasm for Brown. His speech last week was dismal and cringe-making when he invoked the Bible to "suffer little children". There seems not the slightest reason to swallow his deluge of new promises when he has had effective charge of Britain's public services for a decade with insignificant success. Yet he has convinced a large part of the electorate that he is possessed of a maturity and grip that Cameron lacks. He is seen to be in control of his own party, while the Tories are stricken by a self-loathing to match that of Labour in the 1980s.

Even if Cameron produces a speech tomorrow that generates rapturous applause, he is unlikely to overcome his dismal poll ratings. I shall vote Tory because I do not believe Brown is capable of leading Labour to self-renewal. In a few months, the country will tire of him - probably, however, after electing for itself five years of dreary, ineffectual Presbyterian nannyism.

Cameron has it in him to become an impressive prime minister. But many of his own party disagree, which is a rotten start to their election campaign. True, old Labour never much cared for Blair. But by 1997 the electorate was heartily sick of Major, while today they are absurdly enthused about Brown. Even if Cameron fights a storming election campaign, he will be wise to keep twisting his head to check whether it is still attached to his shoulders. The guillotine beckons before a protesting William Hague succeeds to the hollow crown.